Ion Trap with Elongated Electrodes

ABSTRACT

An ion trap 1 comprises one ejection electrode 2 for ion trapping having an opening 4, through which ions in the ion trap 1 can be ejected in an ejection direction E and further electrodes 3 for ion trapping, wherein the ejection electrode 2 and the further electrodes 3 are elongated in a longitudinal direction L. The angle α between the longitudinal direction L and the ejection direction E is nearly  90°.  The ion trap 1 comprises a primary winding 5 connected to an RF power supply 6, a secondary winding 7 coupling with the primary winding 5 for transforming the RF voltage of the RF power supply 6 supplying the transformed RF signals to the ejection electrode 2 and secondary windings 7′ coupling with the primary winding 5 for transforming the RF voltage of the RF power supply 6 supplying the transformed RF signals to the further electrodes 3. The ion trap 1 comprises a first DC supply 8, a second DC supply 9 and a controller 50, which is applying in a time period a first DC voltage provided by first DC supply 8 via the secondary winding 7 to the ejection electrode 2 to pull ions in the ion trap to the opening 4 of the ejection electrode 2 and a second DC voltage provided by the second DC supply 9 via the secondary windings 7′ to the at least  70 % of the further electrodes 3 to push ions in the ion trap to the opening 4 of the ejection electrode 2.

PRIORITY

This application claims priority to UK Patent Application 1907235.4,filed on May 22, 2019, and titled “Ion Trap with Elongated Electrodes,”by Jan Peter Hauschild et al, which is hereby incorporated herein byreference in its entirety.

TECHNICAL FIELD OF THE INVENTION

This invention relates to an ion trap and to a method of ejecting ionsfrom an ion trap, wherein the ions are ejected in an ejection directionE which is perpendicular or substantially perpendicular to thelongitudinal direction L of the ion trap.

BACKGROUND OF THE INVENTION

Ion traps could be used in order to provide a buffer for the incomingstream of ions and to prepare a packet with spatial, angular andtemporal characteristics adequate for the specific mass analyser.Examples of pulsed mass analysers include time-of-flight (TOF), Fouriertransform ion cyclotron resonance (FT ICR), Orbitrap® types (i.e. thoseusing electrostatic only trapping), or a further ion trap.

Ion traps are storage devices that use RF fields for transporting orstoring ions. Typically, they include a RF signal generator thatprovides a RF signal to the primary winding of a transformer. Asecondary winding of the transformer is connected to the electrodes(typically four) of the storage device. Typically they comprise elongateelectrodes extended in a longitudinal direction L and the electrodes arepaired along axes perpendicular to the longitudinal direction. In a iontrap having e.g. 4 electrodes the electrodes are shaped to create aquadrupolar RF field with hyperbolic equi-potentials that contain ionsentering or created in the ion trap. Trapping within the ion trap can beassisted by the use of a DC field. As can be seen from FIG. 2a , each ofthe four elongate electrodes is split into three along the z axis.Elevated DC voltages can be applied to the front and back sections ofeach electrode relative to the larger central section, therebysuperimposing a potential well on the trapping field of the ion trapthat results from the superposition of RF and DC field components. RFvoltages may also be applied to the electrodes to create an RF fieldcomponent that assists in ion selection.

In particular there are two types of ion traps having elongatedelectrodes: Linear ion traps comprise straight linear electrodes. Curvedlinear ion traps called C-trap comprise curved electrodes. An ion trapcan have various number of of electrodes. In particular an ion trap haspairs of electrodes. Preferably on ion trap has 4 electrodes (quadrupoleion trap), 6 or 8 electrodes.

This invention is now to related to such ion traps, which are ejectedions which are trapped in the ion trap in an ejection direction E whichis perpendicular or substantially perpendicular to the longitudinaldirection L of the ion trap. Therefore the ion trap comprises oneelectrode, an ejection electrode, which has an opening in the ejectiondirection E. Preferably the opening is positioned in the middle of theejection electrode or at least close to the middle of the electrode. Theopening is in particular positioned in the middle of the ejectionelectrode in its longitudinal direction L or at least close to themiddle of the ejection electrode in its longitudinal direction L.

To eject ions from the ion trap in the ejection direction E differentapproachs are known to apply a DC voltages to the electrodes, preferablyafter the RF voltage trapping the ions in the ion trap has been switchedoff or at least reduced.

Chien et al. are proposing in “Enhancement of resolution inMatrix-assisted Laser Desorption Using an Ion-trap Storage/ReflectronTim-of-flight Mass Spectrometer”, Rapid. Comm. Mass Spectrom. Vol. 7,837-844 (1993) to apply to an electrode, through which the ions areleaving the ion trap a DC voltage which is pulling the ions to the thisejection electrode. On the other hand Fountain et al. “Mass-selectiveAnalysis of Ions in Time-of-flight Mass spectrometry Using an Ion-trapStorage Device”, Rapid. Comm. Mass Spectrom. Vol. 8, 487-494 (1994) toapply to electrode, which is opposite of the electrode, through whichthe ions are leaving the ion trap a DC voltage which is pushing the ionsto the electrode, through which the ions are leaving the ion trap.

In U.S. Pat. No. 5,569,917 is disclosed to apply at the same time toapply to an electrode, through which the ions are leaving the ion trap aDC voltage which is pulling the ions to the this ejection electrode andto the electrode, which is opposite of this electrode, a DC voltage ofopposite polarity which is pushing the ions to the electrode, throughwhich the ions are leaving the ion trap.

A similar approach is also decribed in US 2011/0315873 A1 for an iontrap having elongated electrodes. The details, how to apply DC voltagesto the electrodes to eject ions from the ion trap, are illustratedbelow. Also in this approach voltage difference is applied to theejection electrodes and the electrode opposite of the ejectionelectrode. This approach requires a specific DC voltage supply for thesetwo electrodes.

The effeciency of the ejection of the ions from ion trap using thisapproaches is limited. Not all ions stored in the ion trap can beextracted and transferred e.g. by the accelartion lens to a massanalyser. In particular the efficiency depends on the occurrence ofspace charges in an ion trap and the mass distribution of the stored ionpopulation.

Further a lot of ions pushed to the ejection electrode get lost becausethey hit the edge of the opening of the ejection electrode. This resultsin an increased contamination of the edge which might further influencethe behaviour of the ion trap, in particular during ion ejection.

Due to the mentined problems further the dynamic range and linearity ofmass analysers to which the ejected ions are transferred, is limited.

Another disadvantage of the known approachs to eject ions from ion trapsis that to each electrode of a the ion trap a specific DC voltage has tobe applied which is requiring a lot of DC supply devices and a detailedcontrol of the application of different DC voltages to each DCelectrode. It is an object of the invention to provide an improved iontrap having a higher efficiency of ion ejection.

It is an object of the invention to provide an improved ion trap,wherein the dependence of the efficiency of ion ejection on space chargeis reduced.

It is an object of the invention to provide an improved ion trap,wherein the dependence of the efficiency of ion ejection on the massdistribution within the stored ion population is reduced.

It is an object of the invention to provide an improved ion trap,wherein during the ion ejection the contamination of the opening,through which the ions are ejected is reduced in comparison to ion trapsof the prior art.

It is an object of the invention to provide an improved ion trap, bywhich the dynamic range of a mass analyser can increased, to which theion trap is supplying the ejected ions.

It is an object of the invention to provide an improved ion trap, bywhich the linearity of a mass analyser can increased, to which the iontrap is supplying the ejected ions.

Another object of the invention is to provide an improved ion trap witha simplified voltage supply.

SUMMARY OF THE INVENTION

At least one and preferably all of the objects are solved by an ion trapof claim 1.

The inventive ion trap comprises for ion trapping one ejection electrodeand further electrodes. The ejection electrode and the furtherelectrodes are elongated in a longitudinal direction L. The ion trap maybe a straight linear ion trap or a curved linear ion trap (C-trap). Alsothe ion trap might comprise electrodes with linear and curved portions.The ion trap may be a linear quadrupole ion trap, i.e. having fourelongate electrodes. However, the invention may be applied in ion trapshaving more than four electrodes (e.g. six or eight electrodes). Theelectrodes of the ion trap, the ejection electrode and furtherelectrodes, have preferably the same shape along the longitudinaldirection L of the ion trap. So the longitudinal direction can be (thesame direction along the whole ion trap) a straight line or a curvedline or a partially straight and curved line.

In a specific embodiment, different electrodes of the ion trap can beused as ejection electrode at different instants of time.

The ejection electrode of the ion trap has an opening, through whichions in the ion trap 1 can be ejected in an ejection direction E. Theejection direction E of a package of ejected ions is defined as theaverage direction in which the ions of the package fly when leaving theopening of the ejection electrode. So for an ejected package of ions theejection direction is typically defining the direction of the centralion beam of the ion package. The width of the ion beam perpendicular tothe ejection direction E might still depend on experimental conditions.The ejection direction E of the ejected ions is at least nearlyperpendicular to the longitudinal direction L of the electrodes. Theangle α between the longitudinal direction L and the ejection directionE deviates from 90° typically not more than 15°, preferably not morethan 10° and particularly preferably not more than 5°.

For the ion trapping in the ion trap the electrodes of the ion trap, theejection electrode and the further electrodes, are supplied with a RFvoltage. Some or all electrodes may be during ion trapping also suppliedwith a DC voltage e.g. to create potential walls.

The RF voltage applied to the electrodes is generated by transformingthe RF voltage provided by a RF power supply. This RF power supply isproviding the generated RF signal to a primary winding. Then is primarywinding is inductively coupled with a secondary winding. The RF signalgenerated by transformation in this winding is then supplied to theejection electrode. Futher the primary winding is also inductivelycoupled with other secondary windings. The signal generated bytransformation in these other windings is then supplied to the otherelectrodes of the ion trap.

The power supply of the ion trap is controlled by a controller, whichmay comprise various control means, for example: a processor, switches,and/or software to be executed by the processor and other software andhardware components.

With the RF voltages applied to the electrodes, the ions can be trappedin the ion trap. Optionally, the trapped ions are cooled or thermalisedin the ion trap prior to ejection. For the ejection of the ions from theion trap according to the invention also DC voltages have to be appliedto the electrodes of the ion trap. Typically, they are applied, afterthe RF voltage provided to the electrodes has been switched off. The theinventive ion trap is comprising at least two DC supplies, providing DCvoltages to the electrodes of the ion trap. The application of the DCvoltages is controlled by the control of the ion trap.

For ejection of ions from the ion trap, a first DC voltage provided byfirst DC supply is applied to the ejection electrode. The first DCvoltage is provided to the ejection electrode via the secondary winding,which is also supplying the RF signal to the ejection electrode. Thefirst DC voltage is applied to the ejection electrode to pull the ionsin the ion trap to the opening of the ejection electrode.

A second DC voltage is provided by second DC supply. The second DCvoltage is provided to at least 70% of the further electrodes via thesecondary windings which are also supplying the RF signal to the furtherelectrodes. The second DC voltage pushes ions in the ion trap to theopening of the ejection electrode. Therefore, the DC voltage provided bysecond DC supply to the at least 70% of the further electrodes has thesame polarity as most ions in the ion trap.

Preferably the number of further electrodes is 3, so that the ion trapis a quadrupole. But the number of the further electrodes could be alsoin other embodiments 5 (heaxpole) or 7 (octopole).

In a preferred embodiment the ion trap comprises curved electrodes. Inparticular the inventive ion trap can be a curved ion trap.

In preferred embodiments of the inventive ion trap the angle α betweenthe longitudinal direction L and the ejection direction E deviates from90° not more than 7°, preferably not more than 3°.

In other preferred embodiment of the inventive ion trap the controlleris applying in the time period the second DC voltage provided by thesecond DC supply via the secondary windings to the at least 80% of thefurther electrodes to push ions in the ion trap to the opening of theejection electrode. In a more preferred embodiment of the inventive iontrap the controller is applying in the time period the second DC voltageprovided by the second DC supply via the secondary windings to allfurther electrodes 3 to push ions in the ion trap to the opening of theejection electrode.

The time period in which the controller is applying the first DC voltageto the ejection electrode and second DC voltage to the furtherrelectrodes, can be between 5 ms and 5000 ms, preferably between 10 msand 2000 ms and particular preferably between 50 ms and 500 ms. Inparticular both DC voltages can be applied at the same time, but theremight be a delay up to 5000 ns, preferably up 500 ns and in particularpreferably up to 100 ns. Preferably the second voltage is at firstapplied to the further electrodes.

Typically, is voltage difference between the first DC voltage applied tothe ejection electrode 2 and the second DC voltage applied to thefurther electrodes 3 between 50 V and 800 V, preferably between 100 Vand 600 V and particular preferably between 200 V and 400 V.

The inventive ion trap comprises in a preferred embodiment a focusinglens, which is arranged for the ejected ions downstream of the of theopening of the ejection electrode and is focusing the ejected ions.Preferably the focusing lens has an opening into which the ejected ionsare directed which is larger than the opening of the ejection electrode.The focusing lens 10 may be an electrostatic lens to which a DC voltageis applied. Typically is the voltage difference between the DC voltageof the focusing lens and the first DC voltage of the ejection electrodeis between 250 V and 1,500 V, preferably between 400 V and 1,000 V andparticular preferably between 600 V and 800 V. Typically the ratio ofthe voltage difference between the DC voltage of the focusing lens andthe first DC voltage of the ejection electrode and the voltagedifference between the first DC voltage applied to the ejectionelectrode and the second DC voltage applied to the further electrodes 3is between 1.5 and 6, preferably between 2.0 and 4 and particularpreferably between 2.2 and 3.

The inventive ion trap comprises in a preferred embodiment anacceleration lens, which is arranged for the ejected ions downstream ofthe focusing lens. The acceleration lens 12 has preferably an opening 13into which the ejected ions are directed which is smaller than theopening of focusing lens. the acceleration lens 12 Preferably is theacceleration lens an electrostatic lens to which a DC voltage isapplied. Typically the voltage difference between the DC voltage of theacceleration lens and the DC voltage of the focusing lens is between 800V and 5,000 V, preferably between 1,500 V and 3,500 V and particularpreferably between 2,000 V and 2,700 V. Typically is the ratio of thevoltage difference between the voltage difference between the DC voltageof the acceleration lens and the first DC voltage of the ejectionelectrode and the voltage difference between the first DC voltageapplied to the ejection electrode and the second DC voltage applied tothe further electrodes between 2 and 12, preferably between 4 and 9 andparticular preferably between 5 and 7. Typically is the ratio of thevoltage difference between the first DC voltage applied to the ejectionelectrode and the second DC voltage applied to the further electrodesand the voltage difference between the voltage difference between the DCvoltage of the acceleration lens and the second DC voltage applied tothe further electrodes and is between 0.05 and 0.4, preferably between0.1 and 0.25 and particular preferably between 0.12 and 0.2.

In a preferred embodiment of the ion trap the secondary windingsupplying the transformed RF voltage to the ejection electrode and thesecondary winding supplying the transformed RF voltage to one of thefurther electrodes are a pair of secondary windings connected in series.

In a preferred embodiment of the ion trap the secondary windingssupplying the transformed RF voltage to two of the further electrodes 3are a pair of secondary windings connected in series.

In preferred embodiment of the inventive ion trap further components ofa mass spectrometer, in particular a HCD cell or a transport multipole,are supplied with a RF voltage, by tapping RF voltages from the RFsupply of the ejection electrode 2 and further electrodes 3 of the iontrap. Preferably an inductance divider is used for tapping the RFvoltage.

At least one and preferably all of the objects are solved by a method ofelecting ions from an ion trap of claim 23.

The ion trap comprises one ejection electrode and further electrodeselongated in a longitudinal direction L for ion trapping, wherein theejection electrode comprises an opening, through which ions in the iontrap can be ejected in an ejection direction E, wherein an angle αbetween the longitudinal direction L and the ejection direction Edeviates from 90° not more than 15°, wherein RF voltage is supplied tothe ion trap by a primary winding connected to an RF power supply, asecondary winding coupling with the primary winding transforming the RFvoltage of the RF power supply 6 and supplying the transformed RFvoltages to the ejection electrode and secondary windings coupling withthe primary winding transforming the RF voltage of the RF power supplyand supplying the transformed RF voltages to the further electrodes, afirst DC supply 8 and a second DC supply 9.

The methods comprises the first step of switching off the RF voltagesupplied to the one ejection electrode and the further electrodes of theion trap and then in a second step applying in a time period a first DCvoltage via secondary winding provided by the first DC supply to theejection electrode to pull ions in the ion trap to the opening of theejection electrode and a second DC voltage provided by the second DCsupply via the secondary windings to the at least 70% of the furtherelectrodes to push ions in the ion trap to the opening 4 of the ejectionelectrode.

Further details of the inventive method can be derived from thisspecification.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the ejection of ions from an ion trap according to theprior art.

FIG. 2 shows the ejection electrode of an ion trap with elongatedelectrodes.

FIG. 3 shows more detailed electrical circuit of the voltage supply ofanother ion trap according to the prior art, which is a linear ion trap.

FIG. 4 shows more detailed electrical circuit of the voltage supply ofanother ion trap according to the prior art, which is a curved ion trap.

FIG. 5 shows detailed electrical circuit of the voltage supply of afirst embodiment of an inventive ion trap.

FIG. 6 shows the ejection of ions from a second embodiment of aninventive ion trap.

FIG. 7 shows the detailed electrical circuit of the voltage supply of afirst embodiment of an inventive ion trap shown in FIG. 5 including alsoan RF voltage supply for HCD cell and transport multipole.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows the ejection of ions from an ion trap according to theprior arthaving elongated electrodes in the longitudinal direction L. Across section of the ion trap perpendicular to the longitudinaldirection L is shown. The ion trap is comprising an elongate ejectionelectrode 2 and three further elongate electrodes 3. The ejectionelectrode 2 has an opening 4 through which ions stored in the ion trap 1can be ejected in an ejection direction E. In this drawing further isshown the DC voltage supply to the electrodes of the ion trap when ionsshall be ejected. The ejected ions are accelerated from the opening 4 ofthe ion trap to an acceleration lens 12 having an opening 13. At leastan RF voltage is applied to the four electrodes 2,3 of the ion trap,when ions are trapped. It is further possible to apply a small DCvoltage to at least one of the electrodes 2,3 of the ion trap to improvethe trapping by potential wells. Axial trapping is enabled by applyingDC voltages to the end apertures of the trap (not shown).

When the trapped ions are to be ejected, the RF voltage and if presentalso the small DC voltage is switched off. Then an offset voltageV_(acc) is applied via an offset DC source which is positioned betweenthe lower further electrode 3 and the acceleration lens 12, which isgrounded. The same offset voltage V_(acc) (now shown) is also suppliedto the upper further electrode 3. A typical value for the applied offsetvoltage is 2,200 V. Via a first DC supply 8 a first DC voltage V_(eject)is applied to ejection electrode 2. This first DC voltage V_(eject) isapplied between the lower further electrode 3 and the ejection electrode2 by the first DC supply 8. A typical value for the first DC voltageV_(eject) is 300V, wherein the negative polarity is applied to theejection electrode 2. Due to the ejection electrode 2 also beingconnected to the offset DC source that supplies voltage V_(acc),relative to ground a voltage of 1,900 V is applied to the ejectionelectrode 2. Via a second DC supply 9 a second DC voltage is applied toleft further electrode 3, which is arranged opposite to the ejectionelectrode 2 in the ion trap. In the shown example second DC voltage hasthe same value V_(eject) as the first DC voltage. This second DC voltageis applied between the lower further electrode 3 and the left furtherelectrode 3′ by the first DC supply 9. Then the value of the second DCvoltage is also 300V, wherein the positive polarity is applied to theleft further electrode 3′. Due to the ejection electrode 2 also beingconnected to the offset DC source that supplies voltage V_(acc),relative to ground a voltage of 2,500 V is applied to the left furtherelectrode 3. When these voltages are applied to the electrodes 2,3 ofthe ion trap, positively charged ions are pushed by the voltage appliedto the left further electrode 3 in the direction of the ejectionelectrode 2 and pulled by the voltage applied to the ejection electrode2 to the ejection electrode 2. This effect on the positively chargedions is created by the electric field in the ion trap, which is providedby the voltage difference between the left further electrode 3 and theejection electrode 2. This electric field has in particular a componentdirected to the ejection electrode 2 and as shown by the ion beam 32 ofthe ions in the ion trap is directed to the opening 4 of the ejectionelectrode 2. But not all ions are ejected through the opening and arefurther accelerated by the acceleration lens 12. A portion of ionsstrike the edge of the opening 4. This leads to a reduced efficiency ofthe ion ejection and to a contamination of the ejection electrode 2 atthe edge of its opening. Further, a small dotted circle shows thecentral region from which ions are ejected from the ion trap 1, when theDC voltages are applied as described before.

FIG. 2 shows the ejection electrode 2 of an ion trap with elongatedelectrodes. The ejection electrode in elongated in the longitudinaldirection L. Also shown is opening 4 provided in the ejection electrode.Through this aperture 4 ions trapped in the ion trap 1 can be ejected byapplying the DC voltages to the ejection electrode 2 and also furtherelectrodes 3 of the ion trap 1. It is shown that the ions are ejectedfrom the ion through the opening 4 into an ejection direction E. It isshown, that the ejection direction E of the ejected ions issubstantially perpendicular to the longitudinal direction L of theelectrodes. In general, the ejection direction E of the ejected ions isat least nearly perpendicular to the longitudinal direction L of theelectrodes. The angle α between the longitudinal direction L and theejection direction E deviates from 90° typically not more than 15°,preferably not more than 10° and particular preferably not more than 5°.

FIG. 3 shows in more detail an electrical circuit of the voltage supplyof the ion trap 1 according to the prior art disclosed in US2011/0315873 A1. In this Figure is the voltage supply for a linear iontrap shown.

It is shown the ejection of ions stored in the ion trap 1 in ejectiondirection E. The ion trap is comprising an ejection electrode 2 and thefurther electrodes 3, 3′. To facilitate ejection, a opening 4 isprovided in the ejection electrode 2.

A RF power supply 6 is shown which is connected with a primary winding5. Further three pairs of symmetrical secondary windings 7,7′ are shown,which are coupled with the primary winding 5. A RF switch 20 is shown toswitch off the RF power supplied to secondary windings explained below.A first pair of secondary symmetrical windings 21 is shown which areconnected to the full-wave rectifier 42 to rapidly reduce the RF voltagein the further secondary winding after the switch of the supplied RFvoltage.

A first and a second winding 7′ of a second pair of secondary windingssupplies the further electrodes 3, of the ion trap, which are above themiddle and at the right side of the ion trap 1. A first winding 7′ of athird pair of secondary windings supplies the other further electrode 3of the ion trap below the middle of the ion trap. The second winding 7of a third pair of secondary windings supplies the other ejectionelectrode 2 of the ion trap. As can be seen from FIG. 3, all of thefirst windings of the first, second and third pair of secondary windingsare connected together at the central tap 22 of the first pair ofwindings. However, only the second winding of the first pair is alsoconnected to the central tap 22. The ends of the second of the windings7′ and 7 of the second and third pairs of secondary windings close tothe central tap 22 are instead connected to a DC offset supply.

With the circuit shown in FIG. 3, positive or negative offsets(depending on the polarity of the ions trapped in the ion trap) can beset from DC voltage supplies 24, 25 that are selectable through a DCoffset switch 23. However, rather than simply supply these selected DCoffset voltages directly to secondary windings 7,7′, they are routedthrough further high voltage supply switches 26 and 27. These switches26 and 27 that preferably have low internal resistance may be set suchthat the DC offsets are delivered direct to the secondary windings 7,7′.In an alternative configuration, the switches may be set so thatindependent HV offsets can be applied to the two secondary windings 7,7′ respectively supplying the ejection electrode 2 and the right furtherelectrode 3. In the case of positive ions in the ion trap, a DC pushvoltage supply 9 supplies a large positive voltage through push switch27 that can be set on secondary winding 7′ thereby applying a largepositive potential to the right further electrode 3. This large positivepotential repels ions stored in the ion trap towards the aperture 4provided in opposite ejection electrode 2. A corresponding pull DCvoltage supply 8 supplies a large negative potential through pull switch8 and onto secondary winding 7, thereby applying a large negativepotential on the ejection electrode 2 that will attract ions towards itsopening 4. Accordingly, this arrangement allows either a small DC offsetto be applied to the electrodes 2 and 3 that may be used, for example,to provide a potential well for trapping ions within the ion trap. Thispotential may even, for example, be supplied at the same time as the RFpotential being supplied to the electrodes 2 and 3. When the RFpotential is switched off using switch 20, ions may be ejectedorthogonally from the ion trap by applying the DC push voltage supply 9and pull DC voltage supply 8 to the right further electrode 3 and theejection electrode 2 respectively in addition to applying the DC offsetvoltage from 24 or 25 to all of the electrodes.

FIG. 4. shows detailed electrical circuit of the voltage supply of acurved ion trap 1 (C-trap) according to the prior art. The electricalcircuit for providing the RF voltages and DC voltages is essentially thesame as shown in FIG. 3. The ions are now supplied to the C-trap 1 by atransport multipole 31 to which ions are supplied from an ion source(not shown). The C-trap 1 ejects the trapped ions through the opening 4of the ejection electrode 2 into an Orbitrap® mass analyser.

FIG. 5 shows in detail an electrical circuit of the voltage supply of afirst embodiment of an inventive ion trap 1. The ion trap 1 haselongated electrodes 2,3 in a longitudinal direction L and can be alinear ion trap or a curved ion trap. A cross section of the ion trap 1perpendicular to the longitudinal direction L is shown. The ion trap iscomprising an ejection electrode 2 and three further electrodes 3. Theejection electrode 2 has an opening 4 through which ions stored in theion trap 1 can be ejected in an ejection direction E.

In this drawing further is shown the RF voltage supply to the electrodes2,3 when ions are being trapped and the DC voltage supply to theelectrodes 2,3 of the ion trap when ions are being ejected.

Normally at least an RF voltage of two opposite phases is applied to thefour electrodes 2,3 of the ion trap, when ions are trapped. It isfurther possible to apply a small DC voltage to at least one of theelectrodes 2,3 of the ion trap to improve the trapping by potentialwells (supplied as the LO OFFSET voltage from supply 9).

An RF generator is shown as RF power supply 6, which is connected with aprimary winding 5 of a transformer. This primary winding 5 in thetransformer arrangement is coupled with two pairs of secondary windings34, 35. The first pair of secondary windings 34 is supplying via the twowindings 7′ a transformed RF voltage to the lower further electrode 3and the left further electrode 3 arranged in the ion trap 1 opposite tothe ejection electrode 2. The second pair of secondary windings 35 issupplying via the winding 7 a transformed RF voltage to the ejectionelectrode 2 and via the winding 7′ a transformed RF voltage to the upperfurther electrode 3. Further a low offset DC voltage is optionallyapplied to all electrodes 2, 3 when ions are trapped in the ion trap. Inthis situation a pull switch 26 is opened (lower switch position) and apush (offset) switch 27 is switched on to provide the low offset voltage(OFFSET_LO).

When the controller 50 of the ion trap is switching the voltage supplyof the ion trap 1 to eject ions, the control is switching the RF switch36, the pull switch 26 and the push switch 27. At first the RF switch 36is activated so as to switch off the RF voltage supplied to allelectrodes 2, 3 of the ion trap. Then with a very short delay of 0-1000ns the push switch 27 is activated so as to provide a second DC voltage,a high push voltage (OFFSET_HI) to the further electrodes 3 and theejection electrode 2 via the opened pull switch 26. The value of thepush voltage is typically between 1,500 and 2,500 V, preferably between1,800 V and 2,200 V. Then with a very short delay of 0-1000 ns the pullswitch 26 is activated (upper switch position) so as to provide a firstDC voltage (PULL_DC) to the ejection electrode 2 in addition to the highpush voltage. Due to this DC voltage supply the ions in the ion trap 1are ejected through the opening 4 of the ejection electrode. Moredetails about the ion ejection are explained in FIG. 6.

FIG. 6 shows the ejection of ions from a second embodiment of aninventive ion trap 1. The ion trap has elongated electrodes 2, 3 in thelongitudinal direction L. A cross section of the ion trap perpendicularto the longitudinal direction L is shown. The ion trap comprises anejection electrode 2 and three further electrodes 3. The ejectionelectrode 2 has an opening 4 through which ions stored in the ion trap 1can be ejected in an ejection direction E. In this drawing further isshown the DC voltage supply to the electrodes of the ion trap when ionsare ejected. The ejected ions are accelerated to an acceleration lens 12having an opening 13. Further is shown a focusing lens 10 with anopening 11, which is arranged between the opening of the ejectionelectrode 2 and the acceleration lens 12. Ejection electrode 2, focusinglens 10 and acceleration lens 12 are arranged along the ejectiondirection E, wherein ejected ions first pass the opening 4 of theejection electrode 2, then the opening 11 of the focusing lens 10 andfinally the opening 13 of the acceleration lens 12.

Normally at least an RF voltage is applied to the four electrodes 2,3 ofthe ion trap, when ions are trapped, for example in the manner shown inFIG. 5. It is further possible to apply a small DC voltage to at leastone of the electrodes 2,3 of the ion trap to improve the trapping bypotential wells.

When the trapped ions are to be ejected, the RF voltage and if presentalso the small DC voltage is switched off. Then a second DC voltageV_(acc) is applied via second DC supply 9 which is connected with thethree further electrode 3 and the acceleration lens 12, which isgrounded. The three further electrode 3 are connected with the second DCsupply 9 via secondary windings 7′ of a transformer supplying the RFvoltage to the three further electrodes 3. A typical value for theapplied second voltage is 2,000 V. The second DC supply 9 is alsoconnected to the ejection electrode 2 via a first DC supply 8, whereby afirst DC voltage V_(eject) is applied to ejection electrode 2. Thisfirst DC voltage V_(eject) is applied between the further electrodes 3and the ejection electrode 2 by the first DC supply 8. A typical valuefor the first DC voltage V_(eject) is 300V, wherein the negativepolarity is applied to the ejection electrode 2. Due to this, relativeto ground, a voltage of 1,700 V is applied to the ejection electrode 2.When these voltages are applied to the electrodes 2,3 of the ion trap,positively charged ions are pushed by the voltage applied to the furtherelectrodes 3 in direction of the ejection electrode 2 and pulled by thevoltage applied to the ejection electrode 2 to the ejection electrode 2.This effect on the positively charged ions is created by the electricfield in the ion trap, which is provided by the voltage differencebetween the further electrode 3 and the ejection electrode 2. Thiselectric field has in particular an improved component directed to theejection electrode 2 and in particular an improved component directed tothe opening 4 of the ejection electrode 2. Providing only the ejectionelectrode 2 with a different voltage to the further electrodes 3 createsa more non-uniform electric field than in the prior art. Thus by thecurcature of the equi-potentials of this electric field, strongerfocusing of ions through the opening 4 of the ejection electrode 2 maybe achieved. Such non-uniformity of the electric field within the volumeof the ion trap creates a converging lens that may bring ions from awide region (dashed circle) through the narrow ejection opening 4. Thus,advantages are that a higher amount of ions may be extracted from aregion substantially wider that the ejection opening and contaminationof the ejection electrode around the opening may be reduced.Accordingly, as shown in the Figure, the ion beam 32 of the ions in theion trap is directed to the middle of opening 4 of the ejectionelectrode 2. At least nearly all ions are passing the opening 4 and arefurther accelerated by the grounded acceleration lens 12. In theinventive ion trap 1, preferably ions do not strike the edge of theopening 4 or only a small portion of ions do so. This leads to animproved efficiency of the ion ejection: a contamination of the ejectionelectrode 2 at the edge of its opening 4 can be avoided. Further thedotted circle shows the region from which ions are ejected from the iontrap 1, when the DC voltage is applied as decribed before. In comparisonto FIG. 1 the diameter of the circle is bigger and therefore ions of alarger region in the ion trap are ejected by the inventive ion trap.Further is shown that the ion beam 32 leaving the opening 4 is stronglydiverging. To reduce this the focusing lens is positioned between theejection electrode 2 and the acceleration lens 12. The focusing lens 10has a wide opening 11 with a diameter larger than the opening 13 of theacceleration lens 12 and larger than the opening 4. Typically, voltagesViens between 800 V and 5,000 V are applied to the focusing lens 10 by athird DC voltage supply 40, wherein this voltage is applied between thefocusing lens 10 and the grounded acceleration lens 12. In the shownembodiment a voltages V_(lens) of 2,400 V is applied. Preferably thevoltages V_(lens) is between 1,500 V and 3,500 V. By the application ofthe voltage V_(lens) to the focusing lens a collinear ion beam 32 of theejected ions can be formed.

FIG. 7 shows the detailed electric circuit of voltage supply shown inFIG. 5 wherin further RF voltages are tapped from the RF voltage supplyto provide RF voltages to further components of a mass spectrometer, inthis embodiment a transport multipole and a HCD cell. Still othercomponents of a mass spectrometer can be supplied in the same way with aRF voltage. The common supply of the electrodes of the ion trap andother components has the advantage to reduce the number of RF sourcesand avoid synchrosation problems between the ion trap and othercomponents which are influencing the performance of mass spectrometer.Several of the processes of the inventive method can be supported orimplemented using one or more computers and processesors, being standalone or connected or in a cloud system, and by software to execute theprocesses.

The embodiments described in this application represent examples of theinventive ion traps and inventive methods. Accordingly, the inventioncan be realised by each embodiment alone or by a combination of severalor all features of the described embodiments without any limitations.

1. An ion trap comprising: an ejection electrode for ion trapping havingan opening, through which ions in the ion trap can be ejected in anejection direction E; electrodes for ion trapping a primary windingconnected to an RF power supply; a secondary winding coupling with theprimary winding for transforming the RF voltage of the RF power supplyand supplying the transformed RF signals to the ejection electrode;secondary windings coupling with the primary winding for transformingthe RF voltage of the RF power supply and supplying the transformed RFsignals to the further electrodes; a first DC supply; a second DCsupply; and a controller, wherein the ejection electrode and the furtherelectrodes are elongated in a longitudinal direction L, the angle αbetween the longitudinal direction L and the ejection direction Edeviates from 90° not more than 15°, the controller is configured forapplying in a time period a first DC voltage provided by first DC supplyvia the secondary winding to the ejection electrode to pull ions in theion trap to the opening of the ejection electrode and a second DCvoltage provided by the second DC supply via the secondary windings tothe at least 70% of the further electrodes to push ions in the ion trapto the opening of the ejection electrode.
 2. The ion trap according toclaim 1, wherein the ion trap is comprising 3 further electrodes.
 3. Theion trap according to claim 1, wherein the ion trap is comprising 5further electrodes.
 4. The ion trap according to claim 1, wherein theion trap is comprising 7 further electrodes.
 5. The ion trap accordingto claim 1, wherein the ion trap is a curved ion trap.
 6. The ion trapaccording to claim 1, wherein the angle α between the longitudinaldirection L and the ejection direction E deviates from 90° not more than7°, preferably not more than 3°.
 7. The ion trap according to claim 1,wherein the controller is applying in the time period the second DCvoltage provided by the second DC supply via the secondary windings tothe at least 80% of the further electrodes to push ions in the ion trapto the opening of the ejection electrode.
 8. The ion trap according toclaim 7, wherein the controller is applying in the time period thesecond DC voltage provided by the second DC supply via the secondarywindings to all further electrodes to push ions in the ion trap to theopening of the ejection electrode.
 9. The ion trap according to claim 1,wherein the control is applying at the same time a first DC voltageprovided by first DC supply via the secondary winding to the ejectionelectrode to pull ions in the ion trap to the opening of the ejectionelectrode and a second DC voltage provided the second DC supply via thesecondary windings to the at least 70% of the further electrodes to pushions in the ion trap to the opening of the ejection electrode
 10. Theion trap according to claim 1, wherein voltage difference between thefirst DC voltage applied to the ejection electrode and the second DCvoltage applied to the further electrodes is between 50 V and 800 V,preferably between 100 V and 600 V and particular preferably between 200V and 400 V.
 11. The ion trap according to claim 1, wherein the ion trapis comprising a focusing lens, which is arranged for the ejected ionsdownstream of the of the opening of the ejection electrode and isfocusing the ejected ions.
 12. The ion trap according to claim 11,wherein the focusing lens has an opening into which the ejected ions aredirected which is larger than the opening of the ejection electrode. 13.The ion trap according to claim 11, wherein the focusing lens is anelectrostatic lens to which a DC voltage is applied, so that the voltagedifference between the DC voltage of the focusing lens and the first DCvoltage of the ejection electrode is between 250 V and 1,500 V,preferably between 400 V and 1,000 V and particular preferably between600 V and 800 V.
 14. The ion trap according to claim 11, wherein thefocusing lens is an electrostatic lens to which a DC voltage is appliedand the ratio of the voltage difference between the DC voltage of thefocusing lens and the first DC voltage of the ejection electrode and thevoltage difference between the DC voltage applied to the ejectionelectrode and the DC voltage applied to the further electrodes isbetween 1.5 and 6, preferably between 2.0 and 4 and particularpreferably between 2.2 and
 3. 15. The ion trap according to claim 11,wherein the ion trap is comprising an acceleration lens, which isarranged for the ejected ions downstream of the focusing lens.
 16. Theion trap according to claim 15, wherein the acceleration lens has anopening into which the ejected ions are directed which is smaller thanthe opening of focusing lens.
 17. The ion trap according to claim 15,wherein the acceleration lens is an electrostatic lens to which a DCvoltage is applied, so that the voltage difference between the DCvoltage of the acceleration lens and the DC voltage of the focusing lensis between 800 V and 5,000 V, preferably between 1,500 V and 3,500 V andparticular preferably between 2,000 V and 2,700 V.
 18. The ion trapaccording to claim 15, wherein the acceleration lens is an electrostaticlens to which a DC voltage is applied, and ratio of the voltagedifference between the voltage difference between the DC voltage of theacceleration lens and the first DC voltage of the ejection electrode andthe voltage difference between the first DC voltage applied to theejection electrode and the second DC voltage applied to the furtherelectrodes is between 2 and 12, preferably between 4 and 9 andparticular preferably between 5 and
 7. 19. The ion trap according toclaim 15, wherein the acceleration lens is an electrostatic lens towhich a DC voltage is applied, and ratio of the voltage differencebetween the first DC voltage applied to the ejection electrode and thesecond DC voltage applied to the further electrodes and the voltagedifference between the voltage difference between the DC voltage of theacceleration lens and the second DC voltage applied to the furtherelectrodes and is between 0.05 and 0.4, preferably between 0.1 and 0.25and particular preferably between 0.12 and 0.2.
 20. The ion trapaccording to claim 1, wherein the secondary winding supplying thetransformed signal to the ejection electrode and the secondary windingsupplying the transformed signal to one of the further electrodes are apair of secondary windings connected in series.
 21. The ion trapaccording to claim 1, wherein the secondary windings supplying thetransformed signal to two of the further electrodes are a pair ofsecondary windings connected in series.
 22. The ion trap according toclaim 1 at least one of claims 1 to 21, wherein by tapping RF signalsfrom the RF supply of the ejection electrode and further electrodes ofthe ion trap further components of a mass spectrometer, in particular aHCD cell or a transport multipole, are supplied with a RF voltage,wherein preferably an inductance divider is used.
 23. Method of ejectingions from an ion trap, which is comprising one ejection electrode andfurther electrodes elongated in a longitudinal direction L for iontrapping, wherein the ejection electrode comprising an opening, throughwhich ions in the ion trap can be ejected in an ejection direction E,wherein an angle α between the longitudinal direction L and the ejectiondirection E deviates from 90° not more than 15°, wherein RF voltage issupplied to the ion trap by a primary winding connected to an RF powersupply, a secondary winding coupling with the primary windingtransforming the RF voltage of the RF power supply and supplying thetransformed RF voltages to the ejection electrode and secondary windingscoupling with the primary winding transforming the RF voltage of the RFpower supply and supplying the transformed RF voltages to the furtherelectrodes, a first DC supply and a second DC supply, comprising thesteps: switching off the RF voltage supplied to the one ejectionelectrode and the further electrodes of the ion trap; and applying in atime period a first DC voltage via secondary winding provided by thefirst DC supply to the ejection electrode to pull ions in the ion trapto the opening of the ejection electrode and a second DC voltageprovided by the second DC supply via the secondary windings to the atleast 70% of the further electrodes to push ions in the ion trap to theopening of the ejection electrode.